Glass fiber mats and fiber mats made from other synthetic fibers are finding increasing application in the building materials industry, as, for example, in composite flooring, asphalt roofing shingles, siding, and dry wall. The glass fiber mats often replace mats traditionally made using wood, cellulose or asbestos fibers.
Fiber mats, and especially glass fiber mats, usually are made commercially by a wet-laid process, which is carried out on what can be viewed as modified paper making machinery. Descriptions of the wet-laid process may be found, for example, in U.S. Pat. No. 2,906,660 to Hungerford et al., U.S. Pat. No. 3,012,929 to Jackson, U.S. Pat. No. 3,050,427 to Slayter et al., U.S. Pat. No. 3,103,461 to Smith et al., U.S. 3,228,825 to Waggoner, U.S. Pat. No. 3,760,458 to Pitt, U.S. Pat. No. 3,766,003 to Schuller et al., U.S. Pat. No. 3,838,995 to Smith, and U.S. Pat. No. 3,905,067 to Keib et al. In general, the wet-laid process for making glass fiber mats comprises first forming an aqueous slurry of short-length glass fibers (referred to in the art as “white water”) under agitation in a mixing tank, then feeding the slurry onto a moving screen on which the fibers enmesh themselves into a freshly prepared wet glass fiber mat, while excess water is separated therefrom.
Unlike natural fibers such as cellulose or asbestos, glass fibers do not disperse well in water. To overcome this problem, it has been the industry practice to provide suspending aids for the glass fibers. Such suspending aids or dispersants usually are materials that increase the viscosity of the aqueous medium. Suitable dispersants conventionally employed in the art include polyacrylamides, hydroxyethyl cellulose, ethoxylated amines and amine oxides. Other additives such as surfactants, lubricants, and defoamers also have conventionally been added to the white water. Such agents, for example, further aid the wettability and dispersion of the glass fibers. Experience has shown that such additives also often influence the strength of the wet glass fiber mat.
The fiber slurry deposited on the moving screen or cylinder is processed into a sheet-like fiber mat by the removal of water, usually by a vacuum device, and polymeric binder is then applied to the mat. In the manufacture of glass fiber mats, a high degree of flexibility and tear strength is desired in the finished mat in addition to primary dry tensile and wet tensile properties. A binder composition is therefore used to hold the glass fiber mat together. The binder composition is impregnated directly into the fibrous mat and set or cured immediately thereafter to provide the desired mat integrity. The binder composition can be applied to the mat by soaking the mat in an excess of binder solution or suspension, or by impregnating the mat surface by means of a binder applicator, for example, by roller or spray. The primary binder applicator for glass mat machines has been the falling film curtain coater. Suction devices often are also utilized for further removal of water and excess binder and to ensure a thorough application of binder through the glass fiber mat. A widely used binder is based on a urea-formaldehyde (UF) resin commonly fortified with an emulsion polymer. One advantage of urea-formaldehyde resins is that they are relatively inexpensive. In addition to mat strength properties which the binder composition imparts to the ultimately cured mat, the binder also functions to improve the strength of the uncured, wet-laid mat as it is transported from its initial formation into and through the curing oven. Such incipient pre-cured strength is needed to avoid process delays and shutdowns caused by breaks in the endless mat.
The incorporated binder is thermally cured, typically in an oven at elevated temperatures. Generally, a temperature in the range of about 200 to about 250° C. is used during curing. Normally, this heat treatment alone will effect curing of the binder. Catalytic curing, such as is accomplished with addition of an acid catalyst (for example, ammonium chloride or p-toluenesulfonic acid), generally is a less desirable, though an optional, alternative.
Because glass fiber mats made with a binder consisting essentially of a UF resin often are brittle, or because the strength properties of the mats may deteriorate appreciably subsequent to their preparation, especially when the mats are subjected to wet conditions. UF resin binders have commonly been modified by formulating the UF resin with cross-linkers and various catalyst systems or by fortifying the UF resin with a large amount of latex (emulsion) polymer, such as a poly(vinyl acetate), a poly(styrene-butadiene), a poly(styrene-maleic anhydride), a poly(styrene-maleic anhydride-acrylate), or a poly(styrene-acrylate). The use of poly(styrene-butadiene) and related copolymers in urea-formaldehyde resin compositions as a binder for glass fiber mats is disclosed, for example, in U.S. Pat. No. 4,258,098 to Bondoc et al., U.S. Pat. No. 4,560,612 to Yau, and U.S. Pat. No. 4,917,764 to Lalwani et al. The use of poly(styrene-maleic anhydride) copolymers and their hydrolyzed derivatives in urea-formaldehyde resin compositions as a binder for glass fiber mats is disclosed, for example, in U.S. Pat. No. 5,914,365 to Chang et al. The use of (1) poly(styrene-acrylic acid) or poly(styrene-acrylate), (2) poly(styrene-maleic anhydride-acrylic acid), or (3) a physical mixture of (1) and (2) in urea-formaldehyde resin compositions as a binder for glass fiber mats is disclosed in U.S. Pat. No. 6,642,299 of Wertz et al.
The addition of these polymers as a minor component of a urea-formaldehyde resin can improve both the wet and dry tensile properties of the glass mat. However, further improvements in properties are desired. Specifically, some product applications require mats having greater dry tensile strength, greater hot-wet tensile strength, greater elongation at break, greater tear strength, or a combination of two or more of these improved properties. There is also a desire to increase the productivity of methods of manufacturing the glass mats, which would require faster curing times and/or greater hot-wet tensile strength.